Oral tolerance, a term applied to immunologic tolerance toward dietary antigens, is a critical mechanism for avoiding harmful inflammatory reactions toward numerous foreign antigens in the intestine. Dietary antigens may also be an important source of stimulation for T cells systematically and may therefore play a role in shaping the functional phenotype of peripheral T cells. Mechanisms of oral tolerance, and peripheral tolerance in general are poorly understood primarily because until recently it has been impossible to track antigen-specific T cells in vivo. Several years ago our laboratory has developed one solution to this problem by developing an adoptive transfer system of DO11.10 TCR transgenicCD4+ T cells. This proposal describes further methodological advances in the use of this system that now allow direct examination of biochemical activity within individual antigen-specific CD4+ T cells following antigenic stimulation in vivo. Using these methods we would like to characterize the "anergic" state of T cells found in vivo following tolerance induction. Our preliminary data, however, show that tolerance cannot be simply attributed to functional inactivation of antigen-specific T cells, but is also a function of the "tolerized" environment. Using primarily cellular immunology techniques I aim to identify the critical components of what constitutes this environment. The borders between the two specific aims blur in the study of the CD25+ sub-population of antigen-specific CD4+ cells that arise only following tolerogenic antigen exposure, particularly antigen feeding. These cells appear to be both "anergic" and potentially "suppressive". I believe staying under mentorship of Dr. Marc Jenkins represents an ideal situation for this final stage of my development as a fully independent investigator. This laboratory continues to be at the cutting technical edge of studying antigen-specific CD4+ T cell response in vivo. Additional years of mentorship would be helpful since my interests in detailed biochemistry of T cell responses are a relatively recent addition to my past research experiences. I believe extending my training to include attempts to view biological problems in more molecular terms is critical to becoming a well-rounded researcher. Most of the current proposal centers on oral tolerance as a form of systemic immunologic tolerance. However, direct examination of the antigen-specific CD4+ T cell response toward dietary antigen within the intestine itself is an essential part of this proposal. It will also be the main direction of my future investigations. Ultimately, as an academic gastroenterologist I am most interested in applying concepts derived from animal studies toward understanding and therapy of human involving immune dysregulation within the gastrointestinal tract.